Artificial disc prosthesis for replacing a damaged nucleus

ABSTRACT

A multi-piece disc replacement implant for replacing a disc removed by a discectomy including an upper plate member, a lower plate member, and an intermediate resilient member providing movement between the two plate members replicating the natural movement of the spine. The plate members are rigid and have orthogonal sidewalls forming an enclosure. The resilient member is an elastic solid or a multi-chamber balloon structure of fluid-filled sacks that collectively define a non-uniform shape such as an oblate spheroid, or a helically coiled string of beads. Such an implant is capable of supporting the compressive and cyclic loads required of a natural disc. The upper and lower plate members are cooperatively formed to selectively limit the allowable range of motion in any given direction and a provided with protrusions to be received in one or more channels cooperatively formed in the vertebrae and secured in place by a bone screw.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation in part of U.S. patentapplication Ser. No. 12/384,095 filed Mar. 31, 2009 now U.S. Pat. No.8,147,555 which is incorporated herein by reference and which claimspriority from provisional application 61/072,480 filed on Mar. 31, 2008which is also incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to artificial intervertebral disc implantsand, in particular, to a multi-chamber balloon implant that inflates tocreate an oblate spheroid shape.

2. Description of the Background

Intervertebral discs are oblate spherical structures (visibly flattenedat the poles and bulging at the equator) that maintain the space betweenadjacent vertebrae and function as a cushion by absorbing and mitigatingforces acting on the spine as a result of daily activities. Eachintervertebral disc consists of an outer annulus fibrosus, whichsurrounds the inner nucleus pulposus. The annulus fibrosus consists ofseveral layers of strong annular fibrocartilage to contain the nucleuspulposus and distribute pressure evenly across the disc. The nucleuspulposus contains loose fibers suspended in a mucoprotein gel thatserves to absorb shocks and maintain the intervertebral space as thevertebra move relative to one another.

Deterioration of an intervertebral disc can result from disease, traumaor aging, and results in symptoms including limited mobility, and severepain. As a result of normal aging the nucleus pulposus loses its abilityto retain fluid and contracts in volume resulting in a reduction in theintervertebral space. This reduction may put pressure on the nerves ofthe spinal column causing pain. Reduction in volume of the nucleuspulposus also reduces the disc's ability to absorb shock which, coupledwith age or trauma related weakening of the annulus fibrosus oftenresults in a disc herniation. When the annulus fibrosus tears due to aninjury or the aging process, the nucleus pulposus can begin to extrudethrough the tear. This is called disc herniation, a prolapsed disc or,more colloquially, a slipped or ruptured disc. The bulge of a herniateddisc may also put pressure on nearby nerve structures resulting inradiating pain, numbness, tingling, and diminished strength and/or rangeof motion. In addition, the nucleus pulposus contains proteins which, ifextruded from the disc into contact with the neural structures may alsocause inflammation and significant pain.

The majority of minor herniated discs will on their own without surgicalintervention. Physical therapy and pharmaceutical interventions areoften sufficient to manage the condition until this healing can occur.Non-steroidal anti-inflammatory medications are commonly prescribed asare epidural steroid (cortisone) injections, both in conjunction withweight loss and rehabilatory exercise programs. Traditional painmanagement approaches are also applied. In a significant number ofpatients surgical intervention is required when these non-invasivetechniques are unsuccessful.

A wide variety of surgical options are available including laminectomyand discectomy combined with vertebral fusion and/or dynamicstabilization. However, these surgical options are highly invasive andrequire prolonged hospitalization and recovery. More recently,artificial disc replacement prosthetics have been used to replace oraugment all or part of the removed or resected intervertebral disc. Somesuch prosthetics use a ball and socket arrangement. For example, U.S.patent application Ser. No. 10/997,823 for “Articulating Spinal DiscProsthetic” by the inventor herein et al. shows a disc prostheticincluding a superior (upper) plate, inferior (lower) plate, andintermediate layer, in a sandwich. The intermediate member is sandwichedbetween the superior and inferior plate members with conforming sides,and includes a short cylindrical post protruding downward into acircular recess in the inferior plate member to center it and tomaintain a predetermined spacing there between. The post includessnap-in spring fingers that lock into the recess of the inferior memberto prevent withdrawal.

There are also a variety of spring discs that employ springs sandwichedbetween metal endplates. For example, U.S. Pat. No. 5,458,642 to Beer etal. issued Oct. 17, 1995 shows a synthetic intervertebral disc forimplantation in the human body. The disc is comprised of disc-shapedplates 11 joined by springs along the inside. The spring systemdistributes forces acting on the disc between the springs and allowsnormal movement of the vertebrae during flexion and extension of thespine in any direction.

Still other disc prosthetics are soft cushions with material propertiesmore similar to the discs that they replace. Examples of such discreplacements are disclosed in U.S. Pat. Nos. 5,702,450 and 5,035,716,which employ elastic cushion “formed of a disk material with mechanicalproperties as similar as possible to the properties of a natural disk.”

The general concept of an expandable balloon-like artificial discprosthesis filled with a polymer such as silicone is well known. Some ofthese fixate externally to the vertebrae. For example, United StatesPatent Application 20060085074 by Raiszadeh, Kamshad published Apr. 20,2006 shows an expandable intradiscal prosthetic configured to be placedbetween two vertebrae.

United States Patent Application 20070250169 by Lang, Philipp publishedOct. 25, 2007 shows a joint arthroplasty device formed in situ byinserting a hollow device having an aperture and a lumen into a targetjoint, and injecting material into the hollow device to form an implant.

United States Patent Application 20070135922 by Trieu, Hai H. publishedJun. 14, 2007 and his issued U.S. Pat. No. 7,182,783 issued Feb. 27,2007 both show selectively expandable composite structures useful asspinal arthroplasty devices. The structures comprise an outer shellcomprised of a non-hydrogel polymer material. At least one core ispositioned within the outer shell and this may be comprised of ahydrophilic polymer. The core expands upon hydration, thereby deformingthe outer shell.

United States Patent Application 20070073290 by Boehm, Frank H. JR.published Mar. 29, 2007 shows an artificial/prosthetic facet joint withballotable/compressible joint space component composed of latex,polymer, silicone, or any other substance either previously used in theart or not. This flexible outer surface contains within it, aballottable fluid or gelatinous center.

United States Patent Application 20060241759 by Trieu, Hai H. (SDGI)published Oct. 26, 2006 shows oriented polymeric spinal implants whereinthe polymer material is substantially uniformly oriented for increasedstrength perpendicular to the orientation of the polymer material.

United States Patent Application 20060206209 by Cragg et al. publishedSep. 14, 2006 shows a prosthetic nucleus replacement for treating anintervertebral disc. A barrier sealant membrane is deposited on a tissuesurface within a de-nucleated space within an intervertebral disc. Thisis filled with a prosthetic nucleus material.

United States Patent Application 20050149191 by Cragg et al. publishedJul. 7, 2005 shows a spinal mobility preservation apparatus with aproximal body, an intermediate body, a distal body, and an expandablemembrane. The expandable membrane extends into the intervertebral discspace to support the spinal motion segment.

United States Patent Application 20040186576 by Biscup et al. (SpineCo.)published Sep. 23, 2004 shows a prosthetic implant for forming a supportstructure between adjoining vertebrae in a spinal column. The prostheticimplant includes a generally spherical or ellipsoidal body that at leastpartially engages a surface of adjacent vertebrae.

United States Patent Application 20030055506 by Stoy et al. publishedMar. 20, 2003 shows a hydrogel-based prosthetic device for replacing atleast a part of the nucleus of a spinal disc. The prosthetic device iscomposed of at least two essentially parallel soft layers of anelastically deformable hydrogel and at least one rigid layer, the rigidlayer having less compressibility than the soft layers, being adjacentto the soft layers, parallel to them, and firmly attached to them.

U.S. Pat. No. 7,128,746 to Singer et al. (PMT Corporation) issued Oct.31, 2006 shows a method and device for treating human intervertebraldisc herniations using an endoscopic procedure. An access port is openedinto and through the annulus of a disc to remove nucleus pulposus. Aballoon device having a valve structure is positioned via an endoscopicprocedure into the disc space, and the balloon device is filled with aphysiological fluid to occupy the disc interspace or to maintain somedegree of distraction of the created disc space.

U.S. Pat. No. 7,066,960 to Dickman issued Jun. 27, 2006 shows anintervertebral disk prosthesis formed of a matrix of bioincorporablefabric impregnated with a nuclear core mixed into the matrix andhardened. The core is a polymer, preferably of liquid form that curesinto a viscoelastic solid, in which each component—polymer andfabric—reinforces the other against tearing, shearing and weakeningunder stress. Each edge of the outer fabric that interfaces a vertebralend plate is impregnated with an agent to stimulate osseus incorporationand anchoring.

United States Patent Application 20030033017 by Lotz et al. (Univ. ofCalifornia) published Feb. 13, 2003 shows a nucleus implant forrepairing degenerated intervertebral discs that is inflated inside thenucleus space after the degenerated nucleus has been removed tore-pressurize the nuclear space within the intervertebral disc. Theimplant is inflated with a high molecular weight fluid, gel orcombination of fluid and elastomer, through a self-sealing valve thatallows one-way filling of the implant after it is placed within thedisc.

Finally, United States Patent Application 20050033437 by Bao et al.(Pioneer Laboratories, Inc.) published Feb. 10, 2005 shows an artificialdisc device for replacing a damaged nucleus. The device may be insertedinto the natural annulus in a collapsed or compressed state orarrangement and then be expanded. Many variations are shown, one (FIG.34) including opposing spacer plates coupled together at a canister 220with telescoping walls. The canister may be filled with fluid, or may befilled with elastomeric material, or a balloon.

However, none of the preceding inventions presents an ideal replacementfor the natural intervertebral disc is supplants. An ideal replacementwould mimic the properties of the natural disc by maintaining theintervertebral disc space through a full range of natural motion, absorbthe shocks of daily use, permit a natural range of motion and yet resisthyper extension of the joint, limit wear so as to extend the useful lifeof the implant, be collapsible or compressible so as to be implantablethrough minimally invasive techniques and be simple to manufacture andassemble.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the invention to provide an artificialdisc prosthesis that mimics the properties of the natural disc bymaintaining the intervertebral disc space through a full range ofnatural motion, absorbs the shocks of daily use, permits a natural rangeof motion and yet resists hyper extension of the joint, limits wear soas to extend its useful life, is collapsible or compressible so as to beimplantable through minimally invasive techniques and is simple tomanufacture and assemble.

In accordance with one aspect of the present invention, a multi-piecedisc replacement implant device is disclosed for replacing a discremoved by a discectomy. The implant includes an upper plate member, alower plate member, and an intermediate resilient member implantproviding movement between the two plate members replicating the naturalmovement of the spine including flexion/extension, lateral bending, and,in some embodiments, rotation. Each of the plate members are generallyformed to be rigid. The resilient member is an elastic solid or amulti-chamber balloon structure of fluid-filled sacks that collectivelydefine a non-uniform shape such as an oblate spheroid, or a helicallycoiled string of beads. Such an implant is capable of supporting thecompressive and cyclic loads required of a natural disc. The upper andlower plate members are cooperatively formed to selectively limit theallowable range of motion in any given direction.

The various embodiments of the present invention may be implanted byanterior, anterio-lateral, or posterior surgical approach. The size ofeach implant component (in collapsed form) is small enough that they maybe inserted with minimal incisions. Furthermore, the implant componentscan be inserted through the posterior of the spine. A posterior approachto the surgical site reduces the invasiveness of the procedure and mayoften be performed by a single orthopedic surgeon or neurosurgeonwithout a need for a general surgeon which substantially decreases thecost and complexity of the procedure.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features, and advantages of the present invention willbecome more apparent from the following detailed description of thepreferred embodiment and certain modifications thereof, in which:

FIG. 1 is a perspective view of an artificial disc prosthesis accordingto a first embodiment of the present invention.

FIG. 2 is a side view of the disc implant 2 of FIG. 1.

FIG. 3A is a side cross-section of the artificial disc prosthesisaccording to a first embodiment of the present invention.

FIG. 3B is a detail side cross-section of an alternate embodiment of thesidewalls having annular rings at their distal ends so as tointerlocking

FIG. 4 is a perspective view of the multi-chamber balloon includedwithin the prosthesis of FIGS. 1-3.

FIG. 5A is a perspective view of an alternate embodiment of themulti-chamber balloon having a double toroid shape.

FIG. 5B is a side view of an alternate embodiment of a multi-chamberballoon having a double toroid shape.

FIG. 5C is a top view of an alternate embodiment of a multi-chamberballoon having a double toroid shape.

FIG. 5D is a top view of an alternate embodiment of a multi-chamberballoon having a double toroid shape.

FIG. 5E is a top view of an alternate embodiment of a multi-chamberballoon having a double toroid shape.

FIG. 6 is a perspective view of an alternate embodiment of theintervertebral disc implant.

FIG. 7 is a top sectional view of the intervertebral disc prostheticin-situ.

FIG. 8 is a top sectional view of an alternate embodiment of theintervertebral disc prosthetic in-situ.

FIGS. 9A and 9B are opposing perspective views of an upper plate memberaccording to an embodiment of the invention.

FIGS. 10A and 10B are opposing perspective views of a lower plate memberaccording to an embodiment of the invention.

FIG. 11 is a perspective view of an artificial disc prosthesis accordingto an embodiment of the invention.

FIG. 12A is a side view of an artificial disc prosthesis according to anembodiment of the invention.

FIG. 12B is a top view of an artificial disc prosthesis according to anembodiment of the invention.

FIG. 12C is a section through an artificial disc prosthesis according toan embodiment of the invention.

FIG. 12D is an anterior view of an artificial disc prosthesis accordingto an embodiment of the invention.

FIG. 13 is a section view through an artificial disc prosthesisaccording to an embodiment of the invention.

FIG. 14 is a section view through an artificial disc prosthesisaccording to an embodiment of the invention.

FIG. 15 is a top perspective view of another alternative embodiment of amulti-chamber balloon coiled into a helix.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention comprises intervertebral disc implantsincorporating single or multi-chamber balloons of varying shape thatinflate to a unified whole of various forms including regular andirregular oblate spheroids and coiled strings of balloons, any of whichmay be implanted in an anterior, anterior-lateral, or a posteriorsurgical procedure with minimal incisions.

FIG. 1 is a perspective view of the intervertebral disc implant 2according to a first embodiment of the present invention. FIG. 2 is aside view of the disc implant 2 of FIG. 1 and FIG. 3 is a crosssectional view of the disc implant 2 of FIG. 1. With combined referenceto FIGS. 1, 2 and 3, a first embodiment of the present inventionincorporates an upper, or superior, plate member 100, and a lower, orinferior, plate member 102, which are adapted to be secured to upper andlower vertebra, respectively, in a spinal column. A single ormulti-component resilient member 103 (FIG. 3) is also provided, disposedbetween the upper and lower plate members 100, 102. It is to be notedthat the reference to the plate members as upper and lower members isfor the purpose of identifying these members in the drawings. It maywell be possible that the positions of the two plate members are bereversed.

Each of the upper and lower plate members 100, 102 is provided withmeans for securement to the upper and lower vertebra (not shown)including the use of screws through the plate members and into thevertebral body or through tabs affixed to the plate members and into thevertebral body. Also described is the use of posts, spikes or finsaffixed to the top and bottoms surfaces of the plate members forengagement with cooperative holes or slots prepared in the adjacentvertebral body. Plate members 100, 102 may further have theirbone-contacting surfaces manufactured and/or treated or modified tofacilitate or improve bonding to the bone. Several such approaches areknown in the art and should be suitable for use with the presentinvention.

Upper and lower plate members 100, 102 are respectively provided withinterfitted (telescoping) sidewalls 110, 120 extending inward (towardone another) from the opposing surfaces of the plate members to form ahousing for seating and containing the resilient member 103. Thesidewalls 110, 120 are of sufficient height to overlap one another whenthe balloon or resilient member 103 is fully expanded afterimplantation. One or both of the sidewalls 110, 120 may be formed with athicker portion 112 proximal to the plate from which is extends and athinner distal end 114 for overlapping with the opposing sidewall. Thetransition from the proximal portion 112 to the distal portion 114provides a positive stop 116 against which the distal end of theopposing sidewall my rest. The positive stop 116 provides a maximumlimit that the intervertebral disc implant 2 may articulate in aparticular direction as a result of compression of the inner resilientmember 103.

The maximum limit provided by the positive stop 116 may be the same inall directions as depicted in the embodiment of FIG. 1. Alternately, theheight of the proximal portion 112 may be varied about the circumferenceof the intervertebral disc implant 2 as depicted in FIG. 6 to permitrelatively more articulation in, for example, the sagital plane (S) thanin the coronal plane (C). The height of the proximal portion setting theposition of the positive stop 116 in the sagital plane (H2) is less thanthe height of the proximal portion setting the position of the positivestop 116 in the coronal plane (H1) such that greater movement of theupper and lower plate members 100, 102 is permitted. Such variation inheight of the proximal portion 112 is preferable done through acontinuous curve and may permit greater motion in one direction of agiven plane than in another direction (i.e. bending forward is permittedwhile bending backwards is not).

Sidewalls 110, 120 may be formed with annular rings 118 at their distalends as depicted in FIG. 3 b so as to be interlocking thereby preventingthe upper and lower plate members from separating during articulation ofthe spine. As described above with respect to the positive stop 113, theposition of the rings may be varied about the circumferenceintervertebral disc implant 2 to permit relatively more articulation inone plane or direction over another. It should be observed that whilethe depicted embodiment shows the lower sidewall extending outside andover the distal end of the upper sidewall the intervertebral discimplant 2 could be constructed such that the distal end of the uppersidewall extends outside and over the lower sidewall with similarefficacy.

Sidewalls 110, 120 may also be formed, as depicted in FIGS. 1 and 2 witha radial sequence of protruding guides 144 (two are shown) formed in theouter surface of the distal end of sidewall 110. Guides 144 are capturedwithin vertical slots 146 in the sidewalls 120 of the opposing plate102. The protruding guides 144 slide along the vertical slots 146 andprevent relative rotation of the plates 100, 102, but permit a limiteddegree of pivoting flexion. Slots 146 and guides 144 may be utilized inconjunction with or in place of annular rings 118 to also preventseparation of the upper and lower plate members 100, 102 duringarticulation and to control the limits thereof. Variation in the lengthof the slots 146 is used to control the limits of articulation. In apreferred embodiment four slot 146 and guide 144 pairs are implemented,one each at the cardinal points about the intervertebral disc implant 2although more or less, including zero slots/guides may be used.Additionally, walls 110, 120 may be formed with a predeterminedcoefficient of friction on the overlapping portions in order to augmentthe resilient member 103 in controlling or restricting movement betweenthe upper plate 100 and lower plate 102.

With reference to FIG. 3A, the upper plate member 100 preferably has alower surface formed with a concave impression 132 that is complementaryto the shape of the resilient member 103. The lower plate member 102 islikewise preferably formed with a lower surface having a concaveimpression 142 that is similarly complementary to the shape of theresilient member. In a preferred embodiment upper and lower platemembers 100, 102 are circular in plan such that the space enclosed bythe intervertebral disc implant 2 is substantially cylindrical althoughother forms are contemplated as described below. The space enclosed byintervertebral disc implant 2 is occupied by a resilient member 103 asdepicted in FIG. 4.

Resilient member 103 is formed with a generally toroidal member 134(i.e. doughnut shaped) encircling a spherical member 136 that fitswithin a central aperture of the toroidal member 134. The entire member103 (including both members 134 and 136) may be formed as an integralcomponent or as two discrete components that are fitted together assuggested by FIG. 3A. The resilient member 103 may be made of any of avariety of known biocompatible resilient compounds such as siliconerubbers, polyether and polyester urethane, polymethyl methacrylate,polycarbonates and various other polymerizing resins or hydrogels havingthe desired elastic properties. Further, the individual members 134, 136may each be selected from an elastomer having different elasticproperties to achieve the desired operation of the intervertebral discimplant 2 as described blow.

In a preferred embodiment resilient member 103 is formed as amulti-chamber balloon having a toroidal chamber 134 encircling aspherical chamber 136. Both chambers 134, 136 are defined by expandableside walls made, for example, of silicone rubber. Both chambers 134, 136may be inflated either before, or preferably, after implantation. Incombination the inflated chambers of balloon 103 define an oblatespheroid shape which approximates the shape of the disc it is meant toreplace. The chambers may be inflated with air (or another gas) or withany of a variety of liquid or viscous substances as well as curingresins to achieve the desired elastic properties as described. Further,the toroidal chamber 134 and the spherical chamber 136 may each beinflated with different substances to achieve the desired operation.

With reference to FIGS. 9-12, an alternate embodiment of the presentinvention is disclosed having an upper plate member 100 and lower platemember 102 having a generally rounded rectangular shape in plan view.The sidewalls 110 of the upper plate member 100 extend down and receivethe upwardly extending sidewalls 120 of the lower plate member to definean internal void in which the resilient member(s) will be seated. Theanterior sidewalls of both the upper and lower plate members are eachprovided with an opening 90, preferably semi-circular, such that theassembled implant 2 is provided with an aperture 91 through its anteriorface to permit access to the internal void and to the resilient member103 during surgical implantation. The lateral sidewalls of the upperplate member 100 are provided with a shallow recess 216 on their innersurface while the lateral sidewalls of the lower plate member 110 areprovided with a protruding ridge 218 for cooperative engagement with therecess 216 to limit the relative movement of the upper and lower platemembers and prevent the upper and lower plate members from separatingduring articulation of the spine.

In order to secure the prosthesis 102 within the intervertebral space, abore or aperture 304 is provided through each of the upper and lowermembers 100, 102 joining their outer surfaces with the internal void inorder to allow a bone screw 300 to be driven through the plate and intothe bone of the adjacent vertebrae from within the void. A boss or post301 is preferably provided encircling the aperture 304 to reinforce theopening and permit the inner surfaces of the upper and lower platemembers to be formed with a countersink or counter-bore in order torecess the bone screw head so as not to engage the resilient member 103in-situ. The post 301 may also be provided separate and apart from theaperture 304. During a surgical procedure to implant a prosthetic ofthis embodiment, a channel is bored or cut into the surface of theadjacent superior or inferior vertebral body extending from the anteriorface of the bone. The post 301 is received in the channel as theprosthetic is slid into the intervertebral space vacated by the disc.Seating of the post 301 in such a channel resists lateral or posteriortranslations of the device under the loads experienced during the dailyactivities of the patient. A secondary post 302 may be providedextending from the upper and lower surfaces of the upper and lower platemembers, respectively, at the anterior edge of the prosthesis. Thesecondary post 302, if present, is also received within the bored or cutchannel in the bone and serves to resist both lateral translation androtation of the implant during daily use.

In use the resilient member is compressed within the intervertebral discimplant 2 by a retaining clip or similar so as to present a smalleroverall height to ease insertion into the evacuated intervertebralspace. After insertion the clip is removed to permit the resilientmember to expand and the implant to return to its operative dimensions.Where the resilient member is a balloon, the implant may be insertedwith the balloon deflated, the chambers being inflated after the deviceis positioned. Inflation may be accomplished by insertion of a syringe(not shown) through a port 119 in the surface of each chamber so as toinject a fluid or resin filler. Where one or more bone screws are to beused through the upper and/or lower members 100, 102, the balloon mayinserted via aperture 91 and inflated after the prosthetic 2 isimplanted and secured in place

The spherical member 136 when inflated seats itself within the opposingconcave impressions 132, 142, in the upper plate member 100 and lowerplate member 102, respectively. In a preferred embodiment impressions132, 142 are formed with a slightly greater radius (R2) than thespherical member 136 to afford a limited degree of pivoting freedom forflexation. This way, the upper vertebrae may shift either laterally orin a front or rearward direction, relative to the lower vertebrae. Thisflexion is facilitated by the interfitted (telescoping) sidewalls 110,120 extending inward from the major surface of the plates 100, 102. Thetelescoping sidewalls 110, 120 are free to slide together/apart asdescribed. Certain embodiments may include one of only an upper or lowerconcave impression 132, 134.

The spherical member 136 acts a shock absorbing member with the shockabsorbing ability a function of by the elastic properties of the chosenelastomer or balloon material and filler. As the spine is articulated,for example rotated forward in the sagital plane during daily activitythe shoulders 141, 144 of the upper and lower plate members 100, 102formed about the periphery of the concave impressions 132, 142, or theperiphery itself, engages the surface of the torroidal chamber 134. Theelastic properties of the chosen elastomer or balloon material andfiller of the torroidal chamber 134 determine the resistance of theimplant 2 to this flexion. By choosing the relative and absolute elasticproperties of the two resilient members the surgeon may customize theoperational characteristics of the implant as both a shock absorber andan articulating joint to match the natural properties of patientsoriginal intervertebral disc and meet the needs of the patient.

FIG. 5A is a perspective view of an alternative embodiment of aresilient member 203. FIG. 5B is a side view and FIG. 5C is a top viewof this alternate embodiment. The resilient member 203 is formed with adouble toroid member 236, here encircling two spaced spherical chambers234, 238 that fit within spaced central apertures of the toroidalchamber 236. While the term double torroid is used to describe theencircling member, it should be observed that the form need not beprecisely a double torroid in the mathematical sense. Rather, doubletorroid is herein defined to include the join of two closed loops in thesame plane which may ultimately be an ellipse (FIG. 5D), ovoid orrounded rectangle (FIG. 5E) in plan view.

As above, the resilient member 203 may be a balloon wherein thespherical chambers may be integrally formed components with thetorroidal chamber 236 or each may be formed as a discrete component thatis fitted together. The balloon members are constructed from similarmaterials and in a similar manner as the multi chamber balloon of thefirst embodiment of the present invention. The overall shape of theintervertebral disc implant 2 would, of course, no longer be cylindricalbut rather would accommodate the form of resilient member 203. It shouldbe observed that intervertebral disc implant 2, when formed toaccommodate resilient member 203, will have a major and minor axiswhereas the first embodiment, being roughly cylindrical, was symmetricalabout any axis. Spherical chambers 234, 238, being arranged along themajor axis provide relatively more resistance to articulation andflexion about the minor axis such that the surgeon may selectivelyimplant the device with the axis oriented to further provide variableresistance to articulation in one plane over another. FIG. 8 depicts thedevice implanted in the interdiscal space with the major axis orientedin the coronal plane such that rotation in the sagital plane (i.e.medial/dorsal bending) is relatively easier than lateral bending.

FIG. 15 is a top perspective view of another alternative embodiment of amulti-chamber balloon 303 coiled into a helix. The balloon 303 is hereformed with a plurality of spaced spherical chambers 334 connected bycapillary conduits 336 and resembling a string of Christmas lights orbeads. In this case the entire balloon 303 (all chambers 334 andconduits 336) are preferably formed as an integral component from, forexample, silicone rubber. The interior of all chambers 334 and conduits336 remain in fluid communication so that all chambers 334 may beinflated simultaneously via an end conduit 336 having a self sealingport 19. Multi balloon chamber 303 may be incorporated into anintervertebral disc implant 2 in place of the resilient members 103 or203. Alternately, where the nucleus pulpous has been evacuated from theintervertebral disc by the surgeon or otherwise dissipated due to timeor injury but the annulus fibrosus remains substantially intact, theballoon 303 may be inserted directly into the void through an incisionor break in the annulus fibrosus. Once in place it may be inflated toreplace the lost nucleus pulpous. In yet another alternate embodiment asimilar procedure may be performed utilizing a balloon resilient member203 such that the resilient member is inserted with the annulus fibrosusand inflated absent an intervertebral disc implant 2.

In each of the foregoing embodiments, the balloons 103, 203 may beinserted in a deflated state, and later inflated by hypodermic or otherinflation pump to define their respective shapes. One skilled in the artshould now understand that any variety of desired shapes my beestablished with the basic multi-chamber balloon concept, and suchvariations are considered to be within the scope and spirit of thepresent invention. Once inflated, the implants 103, 203 are capable ofsupporting the compressive and cyclic loads required of a natural disc.The size of each implant component (in collapsed form) is small enoughthat they may be inserted with minimal incisions. Furthermore, theimplant components can be inserted through the posterior of the spine. Aposterior approach to the surgical site reduces the invasiveness of theprocedure, and may often be performed by a single orthopedic surgeon orneurosurgeon without a need for a general surgeon, and thussubstantially decreases the cost and complexity of the procedure.

Having now fully set forth the preferred embodiments and certainmodifications of the concept underlying the present invention, variousother embodiments as well as certain variations and modifications of theembodiments herein shown and described will obviously occur to thoseskilled in the art upon becoming familiar with said underlying concept.It is to be understood, therefore, that the invention may be practicedotherwise than as specifically set forth in the appended claims.

I claim:
 1. An implantable prosthetic for replacing an intervertebraldisc of a spinal column, said implantable prosthetic comprising: ahousing enclosing a void, said housing further comprising a monolithicupper housing member having a first upper surface adapted forcooperative engagement with a superior vertebra and a first lowersurface opposite to said first upper surface, a first sidewall extendingdownwardly from a first peripheral edge of said first lower surface andsurrounding the void, a first post extending from a center of said firstupper surface longitudinally in a first direction away from the firstupper surface and away from the void, said first post configured forinsertion within a first channel prepared in said superior vertebra, asecond post at said first peripheral edge extending in a seconddirection away from said first upper surface and from the void parallelto the first direction, said second post configured for engagementwithin said first channel prepared in said superior vertebra, and afirst bore extending from said void through said upper housing memberand longitudinally through said first post for receiving a bone screwconfigured to be driven into said superior vertebra, a monolithic lowerhousing member having a second lower surface adapted for cooperativeengagement with an inferior vertebra and a second upper surface oppositeto said second lower surface, a second sidewall extending upwardly froma second peripheral edge of said second upper surface and surroundingthe void, a third post extending from a center of said second lowersurface longitudinally in a third direction away from the lower surfaceand away from the void, said third post configured for insertion withina second channel prepared in said inferior vertebra, and a second boreextending from said void through said lower housing member for receivinga bone screw configured to be driven into said inferior vertebra, saidfirst sidewall of said upper housing member slideably engaged with saidsecond sidewall of said lower housing member to define said void, aresilient member seated in said void, said resilient member engagingsaid first lower surface of said upper housing member and said secondupper surface of said lower housing member so as to replicate thenatural relative movement of the superior and inferior vertebra; a firstbone screw through and out from said first bore of said upper housingmember and configured to extend into said superior vertebra; and asecond bone screw through and out from said second bore of said lowerhousing member and configured to extend into said inferior vertebra. 2.The prosthetic device of claim 1, wherein said second post is alignedwith said first post along an anterior-posterior axis of said upperhousing member.
 3. The prosthetic device of claim 1, wherein said lowerhousing member further comprises a fourth post at said second peripheraledge and extending in a fourth direction away from said lower surfaceand from the void parallel to the third direction, said fourth postconfigured for engagement within said second channel prepared in saidinferior vertebra.
 4. The prosthetic device of claim 3, wherein saidfourth post is aligned with said third post along an anterior-posterioraxis of said lower housing member.
 5. The prosthetic device of claim 1,wherein said resilient member is further comprised of a plurality ofresilient sub-members.
 6. The prosthetic device of claim 1, wherein saidresilient member comprises a balloon.
 7. The prosthetic device of claim6, wherein said resilient member comprises a balloon having a pluralityof inflatable chambers.
 8. The prosthetic device of claim 7, whereinsaid plurality of inflatable chambers comprised of a first inflatablechamber having a substantially toroidal shape and a second inflatablechamber having a substantially spherical shape, the second inflatablechamber occupying a central void of said toroidal first chamber.
 9. Theprosthetic device of claim 8, wherein at least one of said lower surfaceof the upper housing member and said upper surface of said lower housingmember is formed with a recess substantially in the shape of a sphericalsegment, said recesses engaged by the surface of the spherical secondinflatable chamber.
 10. The prosthetic device of claim 9, wherein saidspherical second inflatable chamber is sized to be seated within saidrecesses.
 11. The prosthetic device of claim 7, wherein said pluralityof inflatable chambers comprised of a first port for inflating a firstinflatable chamber and second port for inflating a second inflatablechamber.
 12. The prosthetic device of claim 7, wherein said plurality ofinflatable chambers comprised of a first inflatable chamber having adouble toroid shape, a second inflatable chamber having a sphericalshape and a third inflatable chamber having a spherical shape, thesecond inflatable chamber occupying a first central void of the firstchamber and the third inflatable chamber occupying a second central voidof the first chamber.